Secondary circuit and timing device for appliance

ABSTRACT

A circuit configuration is disclosed for use in an appliance includes a power switch configured to open and close a first group of electrical contacts, where the contacts while closed cause the appliance to energize upon a user initiating a use of the appliance. The circuit configuration also includes a primary timing device electrically connected to the first group of electrical contacts, the primary timing device being actuated upon energization of the appliance and the primary timing device being configured to de-energize the appliance after a first time period by opening the first group of electrical contacts. The circuit configuration also includes a secondary timing device electrically connected to the power switch by a second group of electrical contacts, where the secondary timing device is configured to de-energize the appliance after a second time period, where the second time period is set based on the first time period.

BACKGROUND

The present invention is directed to a power cut-off circuit configuration, and in particular to a secondary power cut-off device for an appliance, such as a toaster.

Appliances, such as toasters, can utilize heating elements or other components to heat, toast, and/or cook items, such as food to be toasted. Heating elements generally convert electricity into heat by passing the electricity through a metal of high resistivity, causing energy passing therethrough to be converted to heat that is emitted by the heat element. Some examples of heat element materials include Nichrome (nickel and chromium), ceramic materials (such as molybdenum disilicide), polymers, composites, and combinations thereof. During appliance use, one or more heating elements may cause items being heated thereby to become overheated in cases of overuse or malfunction. For example, it can be undesirable to heat a food item too long.

To date, various mechanical and circuit-based configurations have been used to limit the heating and control timing related to appliance misuse or malfunction. For instance, in one example, a thermal sensor is built into an appliance, which can signal to a heating control unit that the item being heated is at risk of being overheated based on a heat and time-based threshold.

SUMMARY

The present invention overcomes shortcomings of the prior art by introducing a secondary circuit configured to automatically break an appliance heating element power circuit after a set time that is preferably chosen to be longer than the maximum time an item can be cooked by the appliance heating element.

According to a first aspect, a circuit configuration is disclosed for use in an appliance. The circuit configuration includes a power switch electrically coupled to a power source, the power switch configured to open and close a first group of electrical contacts, where the contacts while closed cause the appliance to energize upon a user initiating a use of the appliance. The circuit configuration also includes a primary timing device electrically connected to the first group of electrical contacts, the primary timing device being actuated upon energization of the appliance and the primary timing device being configured to de-energize the appliance after a first time period by opening the first group of electrical contacts. The circuit configuration also includes a secondary timing device electrically connected to the power switch by a second group of electrical contacts, where the secondary timing device is configured to de-energize the appliance after a second time period, where the second time period is set based on the first time period, and where the second time period is a third time period longer than the first time period.

According to a second aspect, toaster including a power cut-off function is disclosed. The toaster includes a power switch electrically coupled to a power source, the power switch configured to open and close a first group of electrical contacts, where the contacts while closed cause the appliance to energize upon a user initiating a use of the appliance. The toaster also includes a primary timing device electrically connected to the first group of electrical contacts, the primary timing device being actuated upon energization of the appliance and the primary timing device being configured to de-energize the toaster after a first time period by opening the first group of electrical contacts. The toaster also includes a secondary timing device electrically connected to the power switch by a second group of electrical contacts, where the secondary timing device is configured to de-energize the appliance after a second time period, where the second time period is based on the first time period, and where the second time period is a third time period longer than the first time period.

According to a third aspect, a method for controlling an appliance is disclosed. The method includes receiving an input to energize an appliance, where the appliance includes a heating unit. The method also includes activating a primary timing device of the appliance upon the energizing the appliance, where the primary timing device is connected to a first group of electrical contacts, and where the primary timing device is configured to de-energize the appliance after a first time period by opening the first group of electrical contacts. The method also includes setting a second time period based on the first time period, where the second time period is set to be a third time period longer than the first time period. The method also includes activating a secondary timing device of the appliance upon the energizing the appliance, where the secondary timing device is connected to a second group of electrical contacts, and where the secondary timing device is configured to de-energize the appliance after the second time period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a toaster system including a toaster, according to various embodiments.

FIG. 2A is an example configuration of an appliance power supply circuit, according to various embodiments.

FIG. 2B is a controller circuit for use with power supply circuit in an appliance, according to various embodiments.

FIG. 3 is an embodiment of a transistor-based secondary circuit, according to an aspect of the present invention.

FIG. 4 is a transistor and integrated-circuit-based embodiment of a secondary circuit, according to an aspect of the present invention.

FIG. 5 is another embodiment of a transistor-based secondary circuit, according to an aspect of the present invention.

FIG. 6 is a graph showing a first time period t, a second time period t+n, and a third time period n, according to various embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic representation of a toaster system 10 including a toaster 16, according to various embodiments.

Toaster 16 can be an appliance, as used herein. Toaster 16 can receive an input 12, for example, from a user, computer, or other external source. Input 12 can be received at toaster 16 through various input methods and systems 14, such as buttons, knobs, plungers, levers, etc. Toaster 16 can include a carriage module 18, which can include a ferrous element 20 and an electromagnet 22, which can be used to hold down carriage 18. Electromagnet 22 can be similar to electromagnet 136 of FIG. 2A, described below, according to various embodiments.

Toaster 16 can also include a primary timing device 28, a secondary timing device 32, heating element(s) 30, a controller 26, and a power switch 24. Power switch 24 can be used to regulate power flow from power source 34 to toaster 16, and may be actuated by controller 26 and/or through primary timing device 28 or secondary timing device 32. Additional features and variations on the toaster 16 configuration are contemplated within the scope of this disclosure.

FIG. 2A is an example configuration of an appliance power supply (PS) circuit 100, according to various embodiments. According to the shown example, the circuit can be configured for use in an appliance, such as a pop-up electric toaster (an example of which is schematically shown as toaster 16 of FIG. 1).

PS circuit 100 can be separated into two circuit sub-components, with a heating portion 102 shown at left and an electromagnetic ejection portion 104 shown at right of FIG. 2A. Alternatively, heating portion 102 and ejection portion 104 can compose a single PS circuit 100. Various electrical connection points are represented. A power source 108 can be an alternating current (AC) source, and may be preferably received at either 110-120V or 220-240V, 50-60 Hz, and preferably at a power level of 1100-1300 W, according to various embodiments. A main power switch 110 (e.g., power switch 24 of FIG. 1) can be activated by a user, computer system, or other control according to various embodiments. Where the example appliance is a toaster, pressing down on a carriage lever (e.g., part of carriage module 18 of FIG. 1) may activate power toaster power switch 110.

Power switch 110 may have a first group of electrical contacts including a first pole and a second pole, where the power switch 110 is connected at the first pole to a line 112, and at the second pole to a ground, an inner heater 113 and two outer heaters 111 and 115 connected in series, and a heater relay connection 114. Also connected to the second pole is a PS connection 120, and optionally two resistors shown in box 118, preferably to be utilized where a normally-open relay is employed in circuit 100 in the heating portion 102. Electrically coupled to the resistors in box 118 are line connection 124 and PS connection 126.

The other, ejection portion 104 of PS circuit 100 can preferably include a PS connection 116 with diodes, resistors, capacitors, transistor 134, and at least one electromagnet 136 (e.g., for use in carriage ejection), as shown. A 5V connection 128 and 12V connection 117 may be included, along with a reheat connection 130, a defrost connection 132, and a control connection 122. Control connection 122, reheat connection 130, and defrost connection 132 can be connected to a controller 200, as described in FIG. 2B.

Various circuit components of PS circuit 100 (and other circuits, herein) can be selected such that various specifications of the circuit components is appropriate based on implementation and configuration. Such components could be selected for various configurations by those skilled in the art.

FIG. 2B is a controller circuit 200 for use with power supply (PS) circuit 100 in an appliance, according to various embodiments.

Controller circuit 200 is a primary controller circuit for an appliance, preferably a toaster (e.g., toaster 16 FIG. 1). Controller circuit 200 includes an integrated circuit (IC) (e.g., an application-specific integrated circuit (ASIC)) 210, and connections for the controller circuit 200 to be operatively connected to PS circuit 100 of FIG. 2A. ASIC 210 can have many connections, and can include many IC components, depending on configuration. Examples of ASIC 210 may include ICs, such as commercially-available CMS12560 and/or A0201H timing chips, according to various embodiments. A 5V connection 218 to ASIC 210 can be included, as shown. A reheat connection 212 may be configured to connect to reheat connection 130 of FIG. 1A, a defrost connection 214 may be configured to connect to defrost connection 132 of FIG. 1A, and control connection 216 may be configured to transmit control commands to control connection 122 of circuit 100 of FIG. 1A. Together, circuits 100 and 200 may form a single circuit including both PS and control aspects of an appliance, according to various embodiments.

FIGS. 3-5 are three embodiments of a secondary circuit, according to various embodiments of this disclosure.

FIG. 3 is an embodiment of a transistor-based secondary circuit 300, according to an aspect of the present invention.

An appliance (e.g., toaster 16 of FIG. 1) can include (PS and control) circuits 100 and 200 of FIGS. 2A and 2B, and can operate nominally under standard conditions without further safeguards against overheating. A secondary circuit 300, having an RC circuit 302 and a relay circuit 304, can be introduced in order to prevent overheating of the toaster and/or food item. It is known that toasters employ a timing device to prescribe how long a piece of bread, bagel, etc. should preferably be toasted before ejecting. According to this disclosure, a secondary circuit 300 can be or include a secondary timing device (e.g., circuit 300) in order to act as a power-cutting, circuit-breaking fail safe in a case where a primary timing device fails to operate properly.

When a user operates a toaster including the secondary circuit 300, power switch 110 is closed (e.g., when a toaster carriage having a ferrous element is pressed down) power is applied to the circuit 300, a carriage-holding electromagnet (e.g., 136 of FIG. 2A) is energized and holds the carriage in place, using the ferrous element, against biased ejection springs (not shown). Circuit 300 can include a 12V electrical input 315 at the RC circuit 302 and a 12V electrical input 317 at the relay circuit 304. Both 12V inputs can be connected to and received from PS connection 117, which can be a rectified, tapped a heater winding, filter it and then use it as a 12 volt supply. The carriage can be held down for a set amount of time based on either consumer settings or inputs of external toaster controls at a primary timing device (not shown). In some embodiments, the amount of time can be set by the primary timing device automatically based on conditions or detected requirements. Of note, the secondary circuit 300 (and secondary timing device) can have a time set based on a time set on the primary timing device. For example, a time set on the secondary circuit can be 30 seconds longer than a time period set on the primary timing device. According to various embodiments, there may be a maximum time period setting for the primary timing device. According to another embodiment, a time period setting of the secondary circuit 300 can be set such that it is a time period longer than the longest possible setting of the primary timing device. The delay can be shorter or longer as determined to provide a desired release using relay circuit 304.

At the same time at the carriage is held down and the toaster begins heating operation, a direct current (DC) voltage (e.g., 12V from PS connection 117) can be applied to a secondary circuit 300 (or circuit 400 of FIG. 4, among other embodiments). As shown, transistor Q_(?) 326 can preferably be selected to be a PNP transistor that can operate as normally closed (electrically connected) switches when no bias is applied to the transistor base. Transistor Q_(?) 326 can include a base, an emitter, and a collector. The collector of transistor Q_(?) 326 can be electrically grounded, the base can be connected to a resistor-capacitor (RC) circuit 302, and the emitter can be connected to relay circuit 304. In this case, no bias would be applied at toaster activation due to the RC circuit 302 composed of R₂ at 316 and capacitor C₁ at 320. The RC circuit 302 can be grounded, as shown.

As the RC circuit 302 charges up over time from a biased voltage input (preferably 12V, as shown) from a PS connection 117, e.g., from PS 100 of FIG. 2A, the transistor Q_(?) 326 base becomes increasingly biased (shown also as charge curve 512 of FIG. 5), and transistor Q_(?) 326 having its base connected to the RC circuit 302 and emitter connected to relay circuit 304, can be reached through resistor R₄ 322. RC circuit 203 may have a characteristic charge time “tau,” based on various components' specifications. A reverse-bias Zener diode 318 can be included in RC circuit 302, electrically connected on an output end to resistor R₄ 322 and capacitor C_(?) 324 (leading to transistor Q_(?) 326 and a relay 334 and associated relay switch 332 of relay circuit 304). The Zener diode 318 can be connected on the other end to resistors R2 316 and R3 314 and to capacitor C₁ 320 within RC circuit 302. The Zener diode 318 (with a particular corresponding Zener breakdown voltage) can be placed in the base leg of transistor Q_(?) 326 so that the circuit 300 and transistor Q_(?) 326 do not activate until the specific Zener breakdown voltage has been reached during the RC charge time of RC circuit 302. The characteristic RC charge time may be a function of the various components of RC circuit 302. If the characteristic Zener breakdown is reached, the relay circuit 304 can de-energize a heating element (e.g., 30 of FIG. 1) of an appliance (e.g., toaster 16 of FIG. 1). According to a preferred embodiment, relay 334 can be normally open.

The closed switch 110 condition (see FIG. 2A), once adequate charge is built up in the RC circuit 302, applies voltage to the base of transistor Q_(?) 326, thereby turning transistor Q_(?) 326 “on.” By turning on transistor Q_(?) 326, relay 334 of relay circuit 304 is energized by 12V electrical input 317 from PS 100 connection 117. Relay 334 can be connected in series with the power switch 110. Also as shown, diode D₁ 328 (e.g., a commercially-available standard silicon switching diode, such as a 1N4148 signal diode) is of reverse-bias and is located in a circuit from transistor Q_(?) 326 to ground in order to protect transistor Q_(?) 326 from back electromotive force (EMF) from the relay switch 332 of relay 334. Relay switch 332 is connected to relay 334, which is shown connected to line connection 330 and heater relay connection 336 at two electrical contacts or poles. Line connection 330 and heater relay connection 336 can then be used to de-energize the appliance, as described herein.

Once the RC circuit 302 has been sufficiently charged after a time by 5V input 315, RC circuit 302 can place a bias on the base of transistor Q_(?) 326 which opens the closed switch characteristic of transistor Q_(?) 326, energizing relay 334. As relay 334 is energized, the 12V input from the relay 334 is removed at relay switch 332, thereby shutting down and de-energizing the heating element(s) of the appliance. The RC time constant (e.g., tau) can be chosen to be less than 30 seconds longer than the longest time period of the longest toaster setting, about 30 seconds longer, or more than 30 seconds longer.

Secondary circuit 300 can trigger after the RC time constant is reached, and secondary circuit 300 can remove (de-energize) all AC input power from the various circuit components by opening the power switch 110, and bias can be removed from transistor Q₁ 312 through resistor R₁ 310, causing transistor Q₁ 312 to now operate as a closed switch, allowing capacitor C₁ 320 to discharge through resistor R₃ 314 and thereby removing the bias from transistor Q_(?) 326, and activating (or deactivating) relay circuit 304 accordingly.

FIG. 4 is a transistor and integrated-circuit-based embodiment of a secondary circuit 400, according to an aspect of the present invention.

When the power switch 110 is closed (e.g., when the carriage of a toaster is lowered or pressed down) power is applied to a circuit 400, and the holding electromagnet (e.g., 136 of FIG. 2A or 22 of FIG. 1) is thereby energized. The energized electromagnet can hold the carriage (e.g., carriage module of FIG. 1) in place for a set amount of time, for example based on consumer settings of the external controls. As explained with respect to FIG. 3, a secondary circuit 300 (e.g., a secondary timing device) can include an RC circuit 302 including at least one resistor and at least one capacitor can be configured to set the trigger timing of the circuit. Alternatively, instead of employing an RC circuit 302, the secondary timing device and circuit can include a timer circuit 404 including a timer circuit device, e.g., a “555,” “556,” “558,” or “559” timer integrated circuit, as are commercially available. Examples of timer integrated circuits can include a plurality of transistors, diodes, and resistors on a silicon chip, and can include a plurality of connections, such as grounds, triggers, output, input, control, reset, etc. Based on inputs and configurations, timer circuit 404 can be set for various time periods, including about 30 seconds longer than the longest time period of the longest toaster time setting, less than 30 seconds longer, greater than 30 seconds longer, or any other suitable time longer than the applicable toaster time setting.

As shown in FIG. 4, components including transistor Q_(?) at 410, diode D_(?) at 414, relay at 420, associated relay switch at 416, and line connection at 412 and heate connection at 418 can be similar to the various connections described as to circuit 304 in FIG. 3. However, instead of employing the RC circuit 302 of FIG. 3, FIG. 4, as shown, employs the timer circuit 404 including an integrated timing circuit device 428 configured to set a time period leading to increased appliance control. Also shown are capacitors C_(?) 424, C₂ 432, C₃ 430, resistor R₅ 426, and resistor trigger 422 connected to a positive 12V PS voltage (e.g., VCC) 415, for example from 12V connection 117 ofPS circuit 100 of FIG. 2A. A second PS VCC 419 can also be connected to resistor R5 426 and timing circuit device 428, as shown. As shown the integrated circuit can be in communication with various relays, circuits, and integrated circuit components, both shown and not shown in various embodiments, herein. Fewer overall components may be employed in circuit 400 than circuit 300, according to various embodiments.

As above, the timing circuit, when a time expires at timer circuit 404, a relay signal is sent via first relay connection 417 to second relay connection 411. When second relay connection receives a timer signal from first relay connection 417, transistor Q_(?) 410 activates and allows VCC 413 to energize relay 420, triggering the relay 420 and an associated relay switch 416.

FIG. 5 is another embodiment of a transistor-based secondary circuit 500, according to an aspect of the present invention.

Circuit 500 is another alternative, transistor-based embodiment of a secondary circuit, according to the present invention. Circuit 500 can include various components, as shown, and can be connected to a voltage source at 515 as well as a heating element via line connection 538 and heater connection 542. Circuit 500 can be similar to circuit 300 of FIG. 3, but, as shown, can include additional transistors and other circuitry. Circuit 500 can include a transistor Q₂ 516 having a base, a collector, and an emitter, an RC circuit 544, and components 510 that can be configured to discharge a capacitor C₁ 518 in a case where power has been removed. Components 510 of circuit 500 can include a transistor Q₁ 514, which can be a PNP-type transistor. Transistor Q₁ 514 can have a base, a collector, and an emitter, with the collector connected to base of transistor Q₂ 516. Transistor Q₁ 514 can act as a closed switch connecting capacitor C₁ to ground through resistors R₂ 513 and/or R₃ 512. Resistor R₃ 512 can act as a current-limit resistor protecting transistor Q₁ 514 from high (e.g., short circuit) currents possible during a discharge, for example of capacitor C₁ 518.

Transistor Q₃ 524 can have a base, a collector, and an emitter, as shown. Transistor Q₄ 536 can be a relay coil, and can have a base, a collector, and an emitter, with the collector connected to a relay 534 having a relay switch 540. As shown, resistors R₁ 511 and R₂ 513 form a voltage divider which can be configured to keep a bias on transistor Q₁ 514. As long as AC power is applied at 12V connection 515, the bias on transistor Q₁ 514 keeps transistor Q₁ 514 from conducting. Transistor Q₁ 514 may be configured to conduct only when AC power has been removed. Then transistor Q₁ 514 can discharge capacitor C₁ 518.

Resistor R₃ 513 and capacitor C₁ 518, as shown, form an RC circuit configured to bias transistor Q₂ 516 after a period of time. The period of time should preferably be long enough to charge capacitor C₂ 528 through resistor R₉ 522. Once capacitor C₁ 518 is charged, it can place a bias on transistor Q₂ 516, which can cause transistor Q₂ 516 to stop conducting, thereby disconnecting a input voltage from resistor R₉ 522 and capacitor C₂ 528. As shown, capacitor C₂ 528 and resistor R₁₀ 530 can form an RC circuit 544 that is configured to set the timing for discharging the capacitor C₂ 528. In some embodiments, once capacitor C₁ 518 is charged and has therefore preferably placed a bias on transistor Q₂ 516, capacitor C₂ 528 now can become a power source for circuit 500 until capacitor C₂ 528 is drained of its energy charge.

Resistor R₄ 520 can be a base bias resistor for transistor Q₃ 524, and resistor R₅ 526 can hold the base of transistor Q₃ 524 low when no bias is applied, according to various embodiments. In various embodiments, transistor Q₃ 524 can drive the base of relay coil transistor Q₄ 536 through a resistor R₆ 525, keeping relay coil transistor Q₄ 536 from conducting keeping the relay switch 540 de-energized which can keep relay 534 closed, thereby allowing energy to the heaters via line connection 538 and/or heater connection 542. In a case where capacitor C2 528 has discharged and therefore removed the bias from transistor Q₃ 524, transistor Q₃ 524 may no longer place a bias on the base of relay coil transistor Q₄ 536, causing relay coil transistor Q₄ 536 to begin to conduct, thereby energizing the relay coil transistor Q₄ 536, and opening relay switch 540 via relay 534, which is configured to de-energizes one or more heaters via line connection 538 and/or heater connection 542. Once AC power has been disconnected (preferably through a switch, such as switch 110), then capacitor C₁ 518 can discharge and the process can restart once AC power has been restored to the circuit 500.

Stated different, at an initial appliance (e.g., toaster 16) startup (e.g., when a carriage is initially pressed down by a user), the base of transistor Q₂ 516 can be held low by resistor R₃ 512 and capacitor C₁ 518. For example, capacitor C₁ 518 initial voltage condition can preferably be 0V. This setup can preferably allow voltage to pass through transistor Q₂ 516 to charge capacitor C₂ 528. As shown, resistor R₉ 522 can be a current-limiting resistor configured to protect transistor Q₂ 516 from excessive current due to example initial charge of 0V on capacitor C₂ 528. Once capacitor C₁ 518 has been charged sufficiently to bias transistor Q₂ 516, transistor Q₂ 516 can stop conducting and can in some embodiments effectively disconnects capacitor C₂ 528 from 12V input 515, and capacitor C₂ 528 can begin to deliver the stored energy to transistor Q₃ 524 through the base bias resistor R₄ 520. Capacitor C₂ 528 and resistor R₁₀ 530 form an RC circuit 544 which can set the RC time constant (e.g., “tau”), which can be characteristic of how long the circuit will stay energized. Resistor R₅ 526 can be utilized to hold the base of transistor Q₃ 524 low when no base bias is being delivered.

During a time that the base of transistor Q₂ 516 is forward biased, capacitor C₂ 528 can send a base bias to transistor Q₃ 524, which can turn it on and deliver a base bias to relay coil transistor Q₄ 536. This may preferably prevent relay coil transistor Q₄ 536 from conduction and may hold the energy to the relay 534 (and associated relay switch 540) off. The relay 534 being normally closed can allow voltage to the heater(s) via contact 542 and line contact 538. A resistor R₇ 532 can hold the base of relay coil transistor Q₄ 536 low, preventing it from being biased inadvertently and preferably avoiding false turn-ons in cases where no base bias is present.

In a case where capacitor C₂ 528 and resistor R₁₀ 530 (RC circuit 544) have dumped all their energy and can therefore no longer provide base bias to transistor Q₂ 516, transistor Q₃ 524 can lose its base bias and can shut off. This can have the effect of removing the base bias off of relay coil transistor Q₄ 536, turning it on and allowing the relay 534 to energize, thereby opening the relay 534 (and relay switch 540), shutting power off to the heater(s) via heater contact 542 and/or line contact 538. This power-off condition can remain until power to the circuit 500 is removed or disconnected.

A function of transistor Q₁ 514 can be to turn on when power has been removed from the circuit 500, effectively discharging capacitor C₁ 518. Once capacitor C₁ 518 has been discharged in this way, the described cycle can start again if and when power is restored. The RC timer circuit 544 composed of C₂ 528, and R₁₀ 530 can be charged via 12V connection 515, and can be configured to be set to most any time desired as to when to shut the heaters down.

FIG. 6 is a graph showing a first time period t, a second time period t+n, and a third time period n, according to various embodiments. Primary timing device curve 610 shows an appliance energization curve during normal operation, and secondary timing device curve 612 shows a growing charge (e.g., in the case of an RC circuit such as 302 or 544) where the charge reaches a point and activates a relay, and de-energizes the appliance, as described herein. The curves 610 and 612 may not be drawn to scale, and curve 610 may extend to second time period t+n in a case of malfunction whereby secondary timing device (e.g., 300 or 400) will cause the appliance to de-energize at time t+n, as described herein.

Reference is made herein to the accompanying drawings that form a part hereof and in which are shown by way of illustration at least one specific embodiment. The detailed description provides additional specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The detailed description, therefore, is not to be taken in a limiting sense. While the present disclosure is not so limited, an appreciation of various aspects of the invention will be gained through a discussion of the examples provided.

As used herein, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, time periods, and physical properties are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

The present invention has now been described with reference to several embodiments thereof. The entire disclosure of any patent or patent application identified herein is hereby incorporated by reference. The detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the invention. Thus, the scope of the present invention should not be limited to the structures described herein, but only by the structures described by the language of the claims and the equivalents of those structures. 

1.-20. (canceled)
 21. A control system for an appliance comprising: a power circuit having a first power switch with a first set of electrical contacts that are closed to energizer the power circuit, the electrical contacts of the power switch also configured to selectively provide an electrical connection from the power circuit to energize a heating element; a first timing circuit connected with the power circuit, the first timing circuit energized when the power circuit is energized and configured for controlling a heating time period of a food product, and the first timing circuit configured to send a timer signal for causing the power circuit to de-energize at an expiration of the heating time period; and a second timing circuit connected with the power circuit in parallel with the first timing circuit, the second timing circuit energized when the first timing circuit is energized and configured for timing a secondary time period that is at least as long as the heating time period, and the second timing circuit configured to send a signal for causing the power circuit to de-energize at an expiration of the secondary heating time period.
 22. The control system of claim 21, wherein the first timing circuit and the second timing circuit each comprise an application specific integrated circuit.
 23. The control system of claim 21, wherein the heating time period is configurable by a user.
 24. The control system of claim 21, wherein the secondary heating time period is set to be a maximum time period setting of the appliance.
 25. The control system of claim 21, wherein the first timing circuit is operatively connected with the first power switch for de-energizing the power circuit by opening the first power switch.
 26. The control system of claim 25, wherein the second timing circuit is operatively connected with a second power switch that is connected in series with the first power switch for de-energizing the power circuit by opening the second power switch.
 27. The control system of claim 21, wherein the opening of either of the first and second power switches de-energizes the power circuit.
 28. The control system of claim 21, wherein the first timing circuit is selected from the group consisting of: a resistor-capacitor (RC) circuit, an application-specific integrated circuit, and a transistor based timing circuit.
 29. The control system of claim 21, wherein the second timing circuit is selected from the group consisting of: a resistor-capacitor (RC) timing circuit, an application-specific integrated timing circuit, and a transistor based timing circuit.
 30. A method for controlling a heating time period by an appliance, comprising: closing a power switch to energize an appliance by a power circuit, wherein energizing the power circuit includes energizing a heating element of the appliance; activating two parallel timing circuits upon closing the power switch and energizing the power circuit, wherein the two parallel timing circuits are each connected to the power circuit, and wherein each timing circuit is configured to individually send a timing signal to de-energize the power circuit and thus the heating element; and de-energizing the power circuit at the receipt of a timing signal from one of the two parallel timing circuits.
 31. The method of claim 30, wherein each timing circuit of the parallel timing circuits is selected from the group consisting of: a resistor-capacitor (RC) circuit, an application-specific integrated circuit, and a transistor based timing circuit.
 32. The method of claim 30, further including a step of setting a first time period by a user for a first timing circuit of two parallel timing circuits and for de-energizing the heating element at the expiration of the first time period.
 33. The method of claim 32, wherein the first time period is used to determine a second time period for a second timing circuit of the two parallel timing circuits.
 34. The method of claim 33, wherein the second time period is determined to be at least as long as the first time period.
 35. The method of claim 34, wherein the second time period is set to be a maximum time period setting of the appliance.
 36. The method of claim 30, wherein the step of de-energizing the power circuit comprises energizing a relay to break the power circuit from the heating element.
 37. The method of claim 30, wherein the step of closing the power switch comprises moving an element of the appliance to cause the power switch to close.
 38. The method of claim 37, wherein the moving element comprises a food holding carriage that is held in a heating position by an electromagnet that is also operatively connect with the power circuit. 